The present invention relates to a movable contact unit, which is typically employed in the operation panel of electronic equipment of various types, and a method of manufacturing the same. It also relates to a panel switch using the movable contact unit and a method of manufacturing the same.
In recent years, mobile electronic equipment has expands its type and number. As the electronic equipment becomes compact and lightweight, a smaller and lighter switch has been used for a panel switch for the operation panel of the equipment.
Preferably employed is, in particular, a movable contact unit using a dome-like shaped movable contact that is made of conductive metallic sheet with resiliency. The reason of its popularity is that the movable contact unit can provide: a low profile, positive tactile response in switching operation, and an electrically reliable connection.
Now will be described a conventional movable contact unit and its manufacturing method, and a panel switch using the movable contact unit with reference to FIG. 8 through FIG. 11.
FIGS. 8 and 9 show a sectional view and an exploded perspective view, respectively, of a conventional movable contact unit.
In FIG. 8, base film 51 is formed of an insulating film having flexibility with its outer shape processed into a predetermined shape. Adhesive layer 52, which is formed all over the lower surface of base film 51, adhesively holds each top portion of movable contacts 53 to keep each contact separately. Movable contact 53 is made of conductive metallic sheet having resiliency and is processed into dome-like shape.
Movable contact 53 has, as shown in FIG. 8, truncated cone-shaped peripheral edge 53A and generally spherical-shaped center portion 53B with a slight upward bulge. A drawing process given to the resilient metallic sheet creates smooth contours between center portion 53B and peripheral edge 53A. Separator 54 is made of insulating film 54B having releasable layer 54A on its surface. Movable contact 53 is sandwiched between separator 54 and base film 51. Separator 54 is affixed with adhesive layer 52 lying under base film 51 so that the surface being subjected to the release treatmentxe2x80x94releasable layer 54Axe2x80x94covers all over the lower surface of base film 51.
Separator 54 is tightly affixed with base film 51, preventing movable contact 53 from corrosion and the like. Separator 54 also prevents adhesive layer 52 from accidentally sticking to other portions, or from getting foreign matters thereon during transportation and/or storage.
A conventional movable contact unit is structured above. As shown in the sectional view of FIG. 10, prior to use of such a movable contact unit, after separator 54 is peeled off, movable contacts 53 are affixed to wiring board 56 on which plural fixed contacts 55 (55A and 55B) are disposed so as to correspond each movable contact with the fixed contacts. A panel switch is thus structured.
As illustrated in FIG. 10, each central fixed contact 55A is opposed to the center portion of movable contact 53, and the bottom edge of peripheral portion of movable contact 53 is mounted on each of outer fixed contacts 55B. A panel switch unit is thus configured.
Now will be described how such a switch works.
When a depressing force is exerted on movable contact 53 over base film 51, the dome-like portion of movable contact 53 is flipped with a tactile response. By the flip, a portion, which stays over the top portion of the contact, of the lower surface of base film 51 comes into contact with central fixed contact 55A via movable contact 53, so that electric connections are established between contact 55A and contact 55B.
On the other hand, when the depressing force is released, movable contact 53 is now flipped back to its original shape by its own resiliency to open electrically between contacts 55A and 55B.
As described above, flexible base film 51 has been employed in the conventional movable contact unit and the panel switch using the unit. However, if movable contact 53 is disposed at an area adjacent to the outer edges of base film 51 processed into a predetermined shape, the side of the outer edge of base film 51 has less tightly affixed area. Therefore, an outer edge of adhesive layer 52 under base film 51 cannot hold a tight contact with separator 54 or wiring board 56. Such poor adhesion of base film 51 has often caused lack of sealing.
In particular, in the case that movable contact 53 has not smooth contours between generally spherical-shaped center portion 53B and truncated cone-shaped peripheral edge 53A, for example, having a stepped transitional portion in the contour, base film 51 tends to have an air-contained spot thereunder. This forces manufactures to add an extra step checking the unit for the sealing condition by visual inspection.
Besides, the poor sealing described above further causes an undesired phenomenon: it adversely affects connection reliability of the switch section of the panel switch.
That is, in a movable contact unit having such a poor sealing condition, there is a possibility that foreign matters creep into an opening formed between adhesive layer 52 and separator 54 during transportation and/or storage of the movable contact unit. Another possibility is, as the arrow indicated by a dotted line in the partially enlarged sectional view of the outer shape portion in FIG. 11 shows, foreign matters can enter through an opening between adhesive layer 52 and wiring board 56, after the both has been affixed together.
It is therefore the object of the present invention to provide a highly dustproof movable contact unit and its manufacturing method, and to provide a panel switch using the movable contact unit.
The movable contact unit of the present invention includes a movable contact, a base film, and a separator.
The movable contact is made of resilient conductive metallic sheet, which is formed into a bottom-open, dome-like shape. The base film holds the movable contact with the adhesive layer that is formed under the base film. The base film has sections corresponding to the movable contacts, which are formed into projections fitting with the dome-like shaped movable contact. As for the separator, the release treatment-provided upper surface of the separator is affixed with the adhesive layer lying under the base film. The root portion of the dome-like projection corresponding to the movable contact is tightly affixed to the separator by the adhesive layer under the base film.
The manufacturing method of the movable contact unit of the present invention contains the steps below:
(a) forming the adhesive layer beneath the insulating film-made base film.
(b) allowing the adhesive layer to adhesively hold the top portion of the bottom-open, dome-like shaped movable contact that is made of resilient conductive metallic sheet.
(c) following the step (b), affixing the release treatment-provided upper surface of the separator with the adhesive layer, with the movable contact being sandwiched between the base film and the separator.
(d) following the step (c), applying heat and pressure to the both outer sides of the affixed base film and the separator, thereby:
i) forming the sections corresponding to the movable contacts on the base film into projections fitting with the dome-like shaped movable contact.
ii) firmly affixing the root portion of the dome-like projection that corresponds to the shape of the movable contact to the separator through affixing the adhesive layer to the separator.
The panel switch of the present invention includes a movable contact, a base film, and a wiring board.
In the movable contact unit, the movable contact is made of resilient conductive metallic sheet and is formed into a bottom-open, dome-like shape. The base film of the unit holds the movable contact with the adhesive layer formed beneath the base film. The base film has sections corresponding to the movable contacts, which are formed into projections conforming to the dome-like shaped movable contact. The wiring board has fixed contacts thereon associating with each movable contact. The base film is affixed, with the adhesive layer formed thereunder, to the wiring board.
In addition to the manufacturing steps of the movable contact unit described above, the manufacturing method of the panel switch of the present invention has the steps: i) disposing fixed contacts at positions on the wiring board corresponding to those of the movable contacts of the movable contact unit; ii) peeling off the separator from the movable contact; then iii) affixing the adhesive layer lying under the base film to the wiring board so that the movable contact of the movable contact unit corresponds to the fixed contact on the wiring board.